Re: [PATCH] xen/arm: p2m: Restrict preemption check in apply_p2m_changes

[Ian Campbell <ian.campbell@citrix.com>]

On Tue, 2015-05-05 at 17:31 +0100, Julien Grall wrote:
> Hi Konrad,
> 
> On 05/05/15 16:50, Konrad Rzeszutek Wilk wrote:
> >> ---
> >>  xen/arch/arm/p2m.c | 4 +++-
> >>  1 file changed, 3 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> >> index 65efa94..59dd23a 100644
> >> --- a/xen/arch/arm/p2m.c
> >> +++ b/xen/arch/arm/p2m.c
> >> @@ -948,6 +948,7 @@ static int apply_p2m_changes(struct domain *d,
> >>      const unsigned long sgfn = paddr_to_pfn(start_gpaddr),
> >>                          egfn = paddr_to_pfn(end_gpaddr);
> >>      const unsigned int preempt_count_limit = (op == MEMACCESS) ? 1 : 0x2000;
> >> +    const bool_t preempt = !is_idle_vcpu(current);
> >>      bool_t flush = false;
> >>      bool_t flush_pt;
> >>  
> >> @@ -980,7 +981,8 @@ static int apply_p2m_changes(struct domain *d,
> >>           * always make at least one pass as long as preempt_count_limit is
> >>           * initialized with a value >= 1.
> >>           */
> >> -        if ( count >= preempt_count_limit && hypercall_preempt_check() )
> >> +        if ( preempt && count >= preempt_count_limit
> >> +             && hypercall_preempt_check() )
> > 
> > Could you  use the softirq_pending() check to deal when there are no domains?
> 
> apply_p2m_changes will only be called with no current domain (i.e idle
> vcpu) during DOM0 construction.

I wonder if we could/should try and switch to d0:v0 sooner during the
build process? Is that even feasible?

> If we check softirq_pending for this case, you will Xen will fail to
> build DOM0 but the preemption is not supported.

I also don't really understand how softirq_pending would help here.

Ian.